3D printing design guide

Design custom parts that print cleanly, fit better, and perform more reliably.

This guide is meant to help both new and experienced customers design better FDM parts. Use it to understand tolerances, wall thickness, clearances, strength direction, and the tradeoffs that matter before ordering.

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Key rule Design real clearance into mating parts instead of modeling exact nominal fits.

Key rule Use thicker walls, ribs, and fillets when a part will see load or repeated handling.

Key rule Remember that printed parts are strongest along the printed roads and weaker across layer lines.

Key rule Avoid giant flat unsupported surfaces when a ribbed, curved, or segmented approach would work better.

Quick rules

The fastest way to improve part quality before you order

1. Design real clearance into mating parts instead of modeling exact nominal fits.

2. Use thicker walls, ribs, and fillets when a part will see load or repeated handling.

3. Remember that printed parts are strongest along the printed roads and weaker across layer lines.

4. Avoid giant flat unsupported surfaces when a ribbed, curved, or segmented approach would work better.

Design guidance

Tolerance and fit

FDM is excellent for fast custom parts, but it is not the same process as precision machining. Critical fits should be designed intentionally and, when needed, tested with a small sample or adjusted after printing.

Plan on practical clearance for sliding, snap, and assembled features.
Small printed holes often come out undersize and may need to be drilled or reamed.
If one feature matters more than anything else, call it out early so it can be reviewed.

Design guidance

Strength direction and orientation

Printed plastic behaves differently depending on how the part is oriented. Loads that try to pull layers apart are usually the highest-risk direction.

Think about where the part will bend, pull, or impact in real use.
Move stress away from sharp inside corners and thin transitions.
If a part is structural, use generous fillets, real wall thickness, and sensible geometry changes.

Design guidance

Walls, ribs, and feature sizing

Thin walls may look fine in CAD but still print weakly or inconsistently. Slightly more material often produces a far better real-world part.

Use 1.2 mm as a practical minimum wall and go thicker for durable parts.
Raised or recessed details should be large enough to survive the layer-based process visibly.
Very tiny cosmetic details can disappear or soften during printing.

Design guidance

Hardware, threads, and assemblies

Printed plastic parts work best when they are designed around realistic hardware strategies instead of assuming they behave like machined metal.

Plan for inserts, captured nuts, or post-processed holes where reliability matters.
Repeated screw installation into raw plastic should be approached carefully.
Assemblies usually benefit from designed-in tolerance rather than exact CAD mating surfaces.

Where 3D printing shines

Strengths of the process

Fast iteration without tooling
Complex geometry at low volume
Custom one-off and short-run parts
Fixtures, adapters, housings, and brackets that would be expensive to machine conventionally

What to design around

Tradeoffs to keep in mind

Visible layer lines and process texture
Tolerance limits that are good but not machining-grade
Orientation-dependent strength
Potential warp on large flat or thin geometry

FAQ

Questions that come up during part design

When should I split a part into multiple pieces? Split a design when it exceeds the build volume, when it would be weak in one orientation, or when segmenting it improves finish, strength, or assembly.

How should I handle tight mating features? Design clearance into the CAD first, and if the fit is truly critical, plan for a small test print or light post-processing rather than assuming a perfect nominal fit off the printer.

What if I am not sure my design is printable? You can still upload the file and review the materials and capabilities pages. The quoting flow checks build size automatically, and the design guide helps you spot common geometry issues before ordering.

Next step

Ready to turn the design into a custom part?

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